Cantaluppi, C. J., Retired Area Horticulture Agent, North Carolina Cooperative Extension Service

ABSTRACT

A replicated cultivar trial of Asparagus (Asparagus officinalis) was planted in 2005 with the first harvest starting in 2007 to compare the yields of current cultivars to make recommendations to growers. Cultivars were numerically ranked each year from the highest to lowest yielding. Data is shown through the 2016 harvest. Yield comparisons were made over ten years to determine the longevity of these cultivars.

 

INTRODUCTION

As more people are moving into North Carolina from northern states where asparagus is commonly grown, they look to buy it from local growers here. It is a high-value horticultural crop that is easy to grow and can bring in extra income for growers.

For over 25 years, new asparagus cultivars are being released as male hybrids. Asparagus is normally dioecious, having male and female reproductive structures (flowers) on separate plants. Female plants expend energy to produce seed while in the fern growth stage. Because of this, female plants yield 50-75% less spears than male plants, which produce no seed (Hexamer, 1909). Seeds from female plants fall to the ground and germinate, causing a seedling asparagus weed problem. For this reason, asparagus breeders in the U.S. and other countries have gone with male hybrids obtained from super male parent plants. 

The late Dr. Howard Ellison, former asparagus breeder at Rutgers University, observed that although asparagus produces both male and female plants, about one in 500 male plants would produce male flowers and a few flowers with functional male and female parts.  By selfing flowers on one of these plants, called “hermaphrodites,” Ellison produced his first super male hybrid. When these super males are crossed with a female, the F₁ generation is all male, with no seeds produced. These super male hybrids yield about two to three times the amount of the older dioecious open-pollinated varieties, such as Mary Washington (Garrison, 1991).

Other hybrids are obtained by selecting a male and female parent having good characteristics including spear size, spear quality, yield, and disease resistance. These plants are crossed and the resulting hybrids are evaluated for yield, spear quality, and other essential traits. When two parents that produce good hybrid offspring have been identified, a large number of the male and female parent plants are produced by cloning, in which small pieces of male and female spear tissue are grown separately in tissue culture, which completely regenerates into complete male and female plants that are planted in fields. The root systems or crowns of these plants are dug out of the fields after one year and sold to growers who produce the spears that consumers will buy (Hexamer, 1909).

Spear toughness or tenderness is determined by the tightness of the spear tip, not by spear diameter. A tight spear tip will cause the spear to be tender while a loose tip will cause the spear to be tough and fibrous. As the spear tip opens up or “ferns out”, fiber development starts in the base of the spear to enable the elongated spear to change into a woody stalk to support the weight of the fern, after the harvest season is over. As temperatures increase over 70 degrees F., spears will fern out at shorter heights, causing the grower to pick shorter spears (sacrificing spear height) in order to harvest tender spears of high quality. Under these conditions, a grower will need to pick at least once a day. Under cool temperatures below 70 degrees, spears will elongate more before ferning out, enabling the grower to harvest taller spears with tight tips that remain tender, with the grower picking once every 2-3 days (Motes et al., 1994).

The attributes of the California Hybrids, which are dioecious, should enable the grower to harvest a taller spear (8-9 inches) at temperatures above 70 degrees F. without the tip of the spear opening up or “ferning out”, which causes spears to be tough. Taller spears are heavier, having more weight per spear. The New Jersey male hybrids, University of Guelph male hybrid, and open-pollinated cultivars fern out at a shorter spear height (5-6 inches) under warm temperatures above 70 degrees F. (Cantaluppi and Prescheur, 1997).

In a virgin soil (free of Fusarium), the expected productive life of an asparagus field (any cultivar) is 15-20 years.  Growers feel that peak production occurs in the sixth or seventh year, with the best production occurring during years 7-12. There is a decline of production of about 5% per year in the tenth year and every year thereafter. After the fifteenth year, the field may no longer be economically profitable. Established asparagus growers recover their investment after the fifth year and years 5-10 are their most profitable years (Walsworth, 1995).

The cultivars that were studied in this trial were chosen based on ones that are currently grown for commercial production that are standards in the industry, and ones that may show promise in the future.  The purpose of this trial is to evaluate the longevity of these cultivars by getting a more realistic picture of how they perform over several years.

 

Table 1.  Breeding location and parentage of selected asparagus cultivars.

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Variety             Breeding            Parentage                                                   Comments

                        Location

______________________________________________________________________________

Jersey Giant             NJ             NJ 56 female, NJ 22-8 super male          

Jersey King              NJ             MD 10 female, NJ 22-8 super male           

Jersey Supreme       NJ             NJ 44P female, NJ 22-8 super male         

Jersey Gem              NJ             NJ G27 female, NJ 22-8 super male          

Jersey Knight           NJ              NJ 277C female, NJ 22-8 super male        

UC 157                    CA              F 109 female, M120 male                           dioecious hybrid

UC 115                    CA              F 600 female clone, M256 male clone        dioecious hybrid

Atlas                        CA              F 109 female, unspecified Rutgers male    dioecious hybrid

Apollo                      CA              F 109 female, unspecified Rutgers male    dioecious hybrid

Grande                    CA              F 109 female, unspecified Rutgers male    dioecious hybrid

Purple Passion        CA             Progeny of Violeta d’ Albinga                       burgundy, high sugar

Guelph Millennium   CA            University of Guelph Male Hybrid                              

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MATERIALS AND METHODS

Proper variety selection is important for grower success so a ¼ acre replicated asparagus cultivar trial was planted at the Garnett Carr farm in Roxboro, NC with 12 cultivars. Seeds were sown in the greenhouses of Aarons Creek Greenhouses in Buffalo Junction, VA on January 20, 2005, and 15-week-old seedling transplants were planted into the field on May 4, 2005 in an Appling Sandy Loam soil. A randomized complete block design with 12 plants per plot and 4 replications was used. Transplants were spaced one foot between plants in the row and five feet between rows and planted in the bottom of a 6-inch deep furrow as recommended by Cantaluppi and Motes (Cantaluppi, 1990; Cantaluppi and Prescheur, 1997; and Motes et al., 1994). As new spears emerged, and as new ferns were formed, the furrows were filled in below the lowest fern branchlets until the furrows were completely filled in at ground level. Since the trial was planted using seedling transplants, no harvest was taken in 2006. This was done to build food reserves in the crown of the plant to strengthen the plant for a 2-week harvest in 2007. 

The transplants were irrigated as needed during the first growing season only by hand placement of water out of a hose, at the base of the plants. Irrigation is normally not needed during field establishment and beyond, if establishing a field from crowns (roots) from one-year-old plants in states where the rainfall is 30 inches or more per year (Cantaluppi and Prescheur, 1997). However, irrigation is imperative during the establishment year with seedling transplants, since they do not have a one-year-old established root system that can tolerate periods of drought.  Irrigation is needed in areas where less than 30 inches of rainfall occur per year. Seeds were used to establish this trial because most of the cultivars were not available as one-year- old crowns.

The trial was harvested for two weeks in 2007, four weeks in 2008, six weeks in 2009, eight weeks in 2010, and six weeks from 2011-2016, with the exception of five weeks in 2015 due to a drop in yield among all cultivars possibly caused by dry conditions (Table 2). 

 

Table 2.  Asparagus harvest dates, length of harvest, and number of harvests.

Year	Date of First Harvest	Length of Harvest	Number of Harvests
2007	March 15	2 weeks	10
2008	March 22	4 weeks	21
2009	March 24	6 weeks	36
2010	March 26	8 weeks	41
2011	March 21	6 weeks	32
2012	March 16	6 weeks	32
2013	April 8	6 weeks	36
2014	April 5	6 weeks	25
2015	April 4	5 weeks	27
2016	March 15	6 weeks	33

 

This harvesting frequency was chosen following research recommendations made by Benson and Motes (1982), Motes (Motes et al., 1994), and Cantaluppi (1990) which showed that harvesting asparagus that was established by planting one-year old crowns, one year after planting (the second year), caused no reduction in subsequent yield, but provided the grower with an income one year earlier than did harvesting two years after planting. Also, in the second year after planting (the third year), the average spear weight was found to be significantly greater in plants that were harvested the previous year than in plants not harvested the previous year.  The increase in spear production may be due to the release of buds from suppression by older shoots (Benson and Motes, 1982; Cantaluppi, 1990; and Motes, et al., 1994). 

Asparagus spears will start to emerge from the soil when soil temperatures reach 50 degrees F. Spears can be cut or snapped to produce spears of marketable length, which is usually between 7 and 9 inches, depending on tip tightness. Asparagus spears may be cut below the soil surface with a knife, or they may be hand-snapped above the soil surface. Cutting asparagus requires more labor, but increases yield 20 to 25% because spears are longer.  However, cutting spears below the soil greatly increases the chance of the knife injuring a bud or emerging spear on the same crown (Cantaluppi and Prescheur, 1997).

When hand snapping, the spear usually breaks above the area containing fiber. In other words, the portion of the spear left in the field will be fibrous, while the harvested spear is tender and is completely edible. The small stub left above the soil after snapping dries up and disintegrates. A new spear does not come up at that spot, but comes up from another bud that enlarges on another part of the crown. Snapped asparagus has no trim-off waste and should command a higher price than cut asparagus with white butts (Cantaluppi and Prescheur, 1997). In this trial, it was decided to snap spears instead of cutting because of the above reasons and is the preferred and accepted method by most growers.

 

RESULTS AND DISCUSSION

Yield data was recorded in lbs./acre. This was obtained by dividing the total square feet of one plot row (60), into 43,560 (the number of square feet in one acre) to get 726-60 square foot rows in one acre. Total yield per cultivar was recorded. The harvesting frequency was based on how fast the spears grew, based on air temperatures as previously described, resulting in harvested spears that had tight tips, before they started to fern out.

Observations of the Trial – 2007-2016

Yields increased for most cultivars from 2007 to 2012 but in 2013 and 2014, yields started to decrease dramatically for all cultivars (Table 4). Total yields in 2015 increased dramatically from 2014 and it was the first year to see yield increases since 2012. It was hypothesized that yields decreased during 2013 and 2014 due to the presence of Cercospora needle blight, a fungal disease, which turns the ferns yellow and brown prematurely, and causes reduced yields the following year.

It was originally thought that by spraying fungicides (chlorothalonil) once every other week from early July to late September would be enough to protect the fern from contacting Cercospora. This was found to be untrue because of tremendous fern browning, by allowing too much time to pass between a 2-week fungicide spray interval with rains washing off the fungicide, allowing the ferns to remain unprotected, which failed to keep Cercospora in check.

So it was decided after the 2014 harvest to initiate a new fungicide spray program, starting in early July 2014, with fungicides being sprayed once every week until late September, and alternating chlorothalonil and mancozeb every other week. This tightening up of the spray interval did, indeed, protect the ferns, causing them to remain green well into October, with very little signs of Cercospora observed. 

The increased spraying caused yields to increase in 2015, which reversed the trend of yield decreases since 2013 with 11 out of 12 cultivars showing a yield increase between 9 and 46% as shown in Table 3. This research proves that intensive weekly spraying of the fern is needed from early July to late September in North Carolina to prevent yield losses in the following year. However, it was observed that yields of Guelph Millennium decreased by 67% in 2015, and did not recover from increased fungicide sprays during 2014, possibly due to Cercospora severely weakening the plants.

In 2016, growth of spears was excellent and for most cultivars, yields greatly surpassed the previous year’s yields, due to another year of judicious fungicide spraying to prevent Cercospora needle blight (Table 3). The effect of spraying weekly from early July to late September is clearly shown in the table below:

 

Table 3.  Percent yield Increases in 2015 and 2016 (spraying once a week) as compared with 2014 (spraying every two weeks).

Cultivar	2014 (lbs./A)	2015 (lbs.A)	% Increase	2016 (lbs.A)	% Increase
UC 157 (F1)	2025	2582	22	4335	41
Jersey Giant	1448	2688	46	3893	31
Jersey King	1754	2534	31	4125	39
Jer. Supreme	2625	3278	20	4271	23
UC 115	1276	1409	9	3012	54
Jersey Gem	2042	2664	23	3645	27
Atlas	2362	3554	34	5093	30
Grande	2290	2873	20	4503	37
Apollo	1358	1549	12	3011	49
Jersey Knight	2546	3202	20	4367	27
Purple Pass.	3930	4507	13	4102	-9
G. Millenn.	2779	1864	-67	4164	56

 

In 2016, spraying once every week from early July to late September resulted in yield increases among most varieties similar to 2015 yield increases, with the exception of Purple Passion, which decreased 9%. Guelph Millennium reversed a yield decrease of 67% in 2015 with a yield increase of 56% in 2016.

This was the second year that showed dramatic yield increases by sticking to a strict weekly fungicide spray program from early July to late September to prevent the destructive Cercospora needle blight from weakening the plants that lead to continual yield reductions over time.

In 2015, Purple Passion ranked first for the third year in a row (Table 5). Atlas moved up from fifth to second place.  Jersey Supreme remained in third place as in 2014, remaining very consistent over the years. Jersey Knight held at 4th place as in 2014. Grande rebounded to fifth place. After falling from fifth to tenth place in 2014, Jersey Giant rebounded to sixth place. Jersey Gem remained constant at seventh place.  UC 157 remained constant at eighth place. Jersey King remained constant at ninth place. Guelph Millennium took a nose dive down to tenth place from being in second place in 2014. It is assumed that it was severely weakened by Cercospora. Apollo remained constant at eleventh place. UC 115 remained constant at twelfth place. It is not clear why Purple Passion moved to first place in 2013, 2014, and 2015, after lagging behind other cultivars in previous years. During the 2014 season, Purple Passion and Guelph Millennium remained in first and second place, respectively, as in 2013. Jersey Giant declined from fifth to tenth place.  Most other cultivars moved up in yield ranking with the exception of Jersey King, Grande, and Apollo, which moved down in yield ranking.

In 2016, Grande rose to first place again since 2012, Jersey Supreme rose to second place and is still very consistent. Guelph Millennium jumped from tenth to third place in one year. Atlas dropped to fourth place and Jersey Giant creeped up to fifth place. This was the first time in three years that Purple Passion fell from first to sixth place.  Jersey King and UC 157 stayed the same at seventh and eighth place, respectively. Jersey Knight fell from fourth to ninth place. Jersey Gem and UC 115 stayed the same at tenth and eleventy place, respectively. 

For grower recommendations, Jersey Supreme, Jersey Giant, Jersey King, and Guelph Millennium would be good choices, along with Purple Passion. The California hybrids are not available as one-year-old crowns. Growers will have to purchase seed and grow their own 12-week-old transplants. Grande and Atlas seemed to yield the best of the California hybrids over ten years.

The purpose of this trial was to evaluate the longevity of these cultivars by getting a more realistic picture of how they performed over ten years. It is hoped that this trial has served its purpose well.

 

Table 4.  Asparagus yield and rankings in lbs./acre.

Cultivar

2007

2008

2009

2010

2011

2012

2013

2014

2015

2016

10 yr. Total

Rank

UC 157

1155  a

2385 abc

3848 abc

4397 a

4897 ab

5278 ab

3507 a

2025   b

2582 bcde

4335 ab

34409

8

J. Giant

944 ab

273  ab

4494 abc

5304 a

6021 ab

5390 ab

4601 a

1448   b

2688 bcde

3893 ab

37520

5

J. King

883 abc

2458 abc

3937 abc

3992 a

4902 ab

5701 ab

4233 a

1754   b

2534 bcde

4125 ab

34519

7

J. Sup.

860 abc

2485 abc

4211 abc

4759 a

5696 ab

6273 ab

4794 a

2625 ab

3278 abc

4271 ab

39252

2

UC 115

821 abc

2314 abc

3175  c

4204 a

5102 ab

4154   b

3138 a

1276   b

1409     e

3012   b

28605

11

J. Gem

734 bcd

2071 bc

3442 abc

3712 a

3770   b

457   ab

4178 a

2042   b

2664 bcde

3645 ab

30833

10

Atlas

717 bcd

2523 abc

3987 abc

4716 a

5630 ab

5846 ab

4336 a

2362   b

3554   ab

5093   a

38764

4

Grande

703 bcd

3030  a

4935 a

5195 a

6654   a

6621   a

4926 a

2290   b

2873 bcd

4503   a

41730

1

Apollo

555   cd

1781  c

3550 abc

4204 a

4220 ab

4160   b

3594 a

1358   b

1549   de

3011    b

27982

12

J. Knight

456   de

1604 c

3233  bc

3821 a

4233 ab

5189 ab

4514 a

2546   b

3202 abc

4367  ab

33165

9

P. Pass.

151   ef

1915  bc

3287  bc

3884 a

4436 ab

5280 ab

5251 a

3930   a

4507 a

4102  ab

36743

6

G. Mill.

86     f

2332 abc

4868 ab

6029 a

6560 ab

5293 ab

5212 a

2779 ab

1864 cde

4164 ab

39187

3

¹Cultivars with the same letter within columns are not statistically significant, Duncan’s Multiple Range Test, .05 level.

 

Table 5.  Yearly asparagus cultivar ranking in numerical order, from highest (1) to lowest  (12) yielding.

Cultivar	2007	2008	2009	2010	2011	2012	2013	2014	2015	2016
UC 157	1	6	7	6	8	8	11	8	8	8
Jer. Giant	2	2	3	2	3	5	5	10	6	5
Jer. King	3	5	6	9	7	4	8	9	9	7
J. Supreme	4	4	4	4	4	2	4	3	3	2
UC 115	5	8	12	7	6	12	12	12	12	11
Jer. Gem	6	9	9	12	12	10	9	7	7	10
Atlas	7	3	5	5	5	3	7	5	2	4
Grande	8	1	1	3	1	1	3	6	5	1
Apollo	9	11	8	8	11	11	10	11	11	12
Jer. Knight	10	12	11	11	10	9	6	4	4	9
P. Passion	11	10	10	10	9	7	1	1	1	6
Millennium	12	7	2	1	2	6	2	2	10	3

 

LITERATURE CITED

Benson, B.L., and Motes, J.E. (1982). Influence of harvesting asparagus the year following planting on subsequent spear yield and quality. HortScience 17(5): 744-745.

Cantaluppi, C.J. (1990). Back to the basics-getting started in asparagus production. In: C. Cantaluppi (ed.). Proc. 1990 Illinois Asparagus School Hort. Ser. 85. Coop. Ext. Serv. Univ. of Illinois at Urbana-Champaign.

Cantaluppi, C.J. and Precheur, R.J. (1997). Asparagus production, management, and marketing. Bulletin 826, The Ohio State University Extension, Columbus, OH.

Garrison, S.A. (1991). New hybrid asparagus varieties for the Midwest. In: C. Cataluppi (ed.). Proc 1991 Illinois Asparagus School Hort. Ser. 89. Coop. Exten. Serv. Univ. Illinois at Urbana-Champaign.

Hexamer, F.M. (1909). Asparagus--Its culture for home use and for market. Orange Judd Company, NY.

Motes, J., Cartwright, B., and Damicone, J. (1994).  Asparagus production. OSU Extension Facts F-6018.  Oklahoma Coop. Ext. Serv., Stillwater, OK.

Walsworth, R. (1995).  Personal communication.  48^th Ave., Rt. 1, Mears, MI  49436.

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